A study investigated success and efficiency of second language learners at varying proficiency levels in communicating intended meaning, including examination of factors contributing to communication breakdown and delay. Three groups of adults (native English-speakers and low- and high-proficiency learners of English as a Second Language) performed concept identification tasks for both concrete and abstract concepts. The groups were equally successful in communicating concrete concepts but not abstract concepts. Abstract concepts required more linguistic and cultural knowledge and grammatical accuracy, knowledge of discourse rules, and development of meaningful contexts were often more crucial in communicating them. In addition, constituent features of concrete concepts are generally visual and support agreement more easily. It was also found that the speaker was more likely to fail if the interlocutor did not participate actively by asking questions, rephrasing and repairing speaker utterances, rearranging clues, and synthesizing examples to obtain a pattern of meaning. Efficiency of communication was also found to be greater for concrete than for abstract concepts, attributed to several factors. Errors made within a context were found less distracting to interlocutors than errors in single significant words. Results suggest that negotiation of meaning is a necessary linguistic skill for second language learners. (MSE)